TECHNICAL FIELD
The present disclosure relates to a negative electrode having improved quick
charging performance, while ensuring adhesion, and a method for manufacturing the same.
The present application claims priority to Korean Patent Application No. 10-2020-
0185311 filed on December 28, 2020 in the Republic of Korea, the disclosures of which
10 are incorporated herein by reference.
BACKGROUND ART
As technical development and needs for mobile instruments have been increased,
secondary batteries that is rechargeable and can be downsized and provided with high
15 capacity have been increasingly in demand. In addition, among such secondary batteries,
lithium secondary batteries having high energy density and operating voltage have been
commercialized and used widely.
A lithium secondary battery has a structure including an electrode assembly
having a positive electrode and a negative electrode, each of which includes an active
20 material coated on an electrode current collector, and a porous separator interposed
between both electrodes; and a lithium salt-containing electrolyte injected to the electrode
assembly. The electrode is obtained by applying a slurry including an active material, a
binder and a conductive material dispersed in a solvent to a current collector, followed by
3
drying and pressing.
In general, a secondary battery includes a positive electrode, a negative electrode,
an electrolyte and a separator. The negative electrode includes a negative electrode active
material capable of intercalation/deintercalation of lithium ions released from the positive
5 electrode. For example, a graphite-based active material, such as a natural graphite or an
artificial graphite, may be used as a negative electrode active material.
An artificial graphite is used frequently in the form of secondary particles. For
this purpose, in general, cokes as a raw material of primary particles are granulated to form
secondary particles, and then graphitization is carried out through heat treatment to provide
10 artificial graphite in the form of secondary particles.
However, when using such a conventional process in which the size of primary
particles is not controlled, non-granulated micropowder or micropowder separated from
the secondary particles even after the granulation is generated in a large amount.
Therefore, the resultant negative electrode shows reduced negative electrode adhesion
15 (resistance against detachment of the negative active material particles from the negative
electrode), and the battery may provide poor high-temperature storage performance. In
addition, since the secondary particles include micropowder, the negative electrode has
non-uniform pores and shows increased pore resistance, resulting in degradation of the
quick charging performance of a battery.

WHAT IS CLAIMED IS:
1. A negative electrode, comprising:
a current collector; and
5 a negative electrode active material layer disposed on at least one surface of the
current collector, and having a negative electrode active material layer containing an
artificial graphite, single-walled carbon nanotubes (SWCNTs) and a binder polymer,
wherein the negative electrode active material layer comprises a lower layer region
facing the current collector, and an upper layer region facing the lower layer region and
10 extended to the surface of the negative electrode active material layer,
the content of the single-walled carbon nanotubes is 0.003-0.07 parts by weight
based on 100 parts by weight of the lower layer region,
the single-walled carbon nanotubes have an average diameter of 0.5-15 nm, and
the upper layer region includes no single-walled carbon nanotubes (SWCNTs).
15
2. The negative electrode according to claim 1, wherein the content of the
single-walled carbon nanotubes is 0.005-0.045 parts by weight based on 100 parts by
weight of the lower layer region.
20 3. The negative electrode according to claim 1, wherein the single-walled
carbon nanotubes have the average diameter of 1-10 nm.
4. The negative electrode according to claim 1, wherein at least one of the
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lower layer region and the upper layer region further comprises a spheronized natural
graphite.
5. The negative electrode according to claim 1, wherein at least one of the
5 lower layer region and the upper layer region further comprises any conductive material
other than single-walled carbon nanotubes.
6. A method for manufacturing the negative electrode as defined in claim 1,
comprising the steps of:
10 preparing a slurry for a lower layer containing an artificial graphite, a first binder
polymer, single-walled carbon nanotubes and a first dispersion medium, and a slurry for an
upper layer containing an artificial graphite, a second binder polymer and a second
dispersion medium and including no single-walled carbon nanotubes (SWCNTs);
coating the slurry for a lower layer on one surface of a negative electrode current
15 collector, and coating the slurry for an upper layer on the slurry for a lower layer, at the
same time or with a predetermined time interval; and
drying the coated slurry for a lower layer and slurry for an upper layer at the same
time to form an active material layer,
wherein the content of the single-walled carbon nanotubes is 0.003-0.07 parts by
20 weight based on 100 parts by weight of the total solid content of the slurry for a lower
layer, and the single-walled carbon nanotubes have an average diameter of 0.5-15 nm.